Further comparative studies will be carried out on the nature and the properties of the fibrin resulting from the action of staphylocoagulase and of biothrombin. As a possible clue to differences in aggregation or polymerization patterns, we intend to compare the two fibrins by viscosity determinations and by lignt scattering. Further studies will be made on the comparative action of plasmin on the two fibrins, followed at various time intervals by SDS polyacrylamide gel electrophoresis and by electron micrographs.